The present invention relates to a graphic equalizer for audio equipment usable in automobiles, such as a car stereo.
Audio equipment usable in automobiles typically includes an AM/FM radio, a tape recorder or the like which are often combined in a single unit commonly referred to as a car stereo.
Such audio equipment has become quite popular and increasingly the same high fidelity normally expected from high-quality home audio equipment is now often required in car stereos. It has thus become necessary to increase the sound fidelity in automobile audio equipment and, consequently, equalizers to compensate for sound distortions caused by the acoustical characteristics of the car interior and frequency deviations have come into increasing use.
The graphic equalizer (hereinbelow, abbreviated to "GEQ") is a popular equalizer apparatus which divides the frequency band of audio signals into a large number of frequency subbands or channels and which can vary the frequency characteristics at the respective channels, and thereby change the frequency characteristics over the entire band as desired. In general, the GEQ includes a combination of a simulated inductor and a bridging amplifier which are constructed of operational amplifiers. By disposing such a GEQ in a car stereo, the aforecited fidelity requirements can be met.
The GEQ, however, has quite a large number of variable resistors or switches for adjusting the frequency characteristics of a number of channels as stated above, and considerable skill is often required to operate the GEQ properly. Moreover, even when one has become skilled in operation of the GEQ, the operation is still troublesome and complicated.
Accordingly, the user of the typical GEQ has the considerable burden of repeating the troublesome operation of the GEQ whenever the sound program or mode of operation is changed. This problem is especially acute in automotive audio equipment since the operation of a complicated GEQ may often divert the driver's attention from safe operation of the automobile.
In order to solve such problems, there has been proposed a GEQ wherein data corresponding to various frequency characteristics intended to be attained with the GEQ are set in a memory or the like in advance and, when necessary, the desired frequency characteristics can be attained merely by selecting the appropriate preset data.
Such a GEQ is often referred to as a presetable GEQ and often is used with a car stereo which may simulate a quadraphonic or 4-channel stereo system by dividing each channel of a stereophonic source program by frequency or the like and directing the divided sound signals to separate speakers disposed within four locations within the automobile. In some sound programs, it has become desirable to give rise to a special mood by altering the frequency characteristics by the GEQ and it is also necessary to be able to switch between normal stereophonic sound reproduction and the simulated 4-channel sound depending upon the sound programs or personal tastes.
The typical GEQ has quite a large number of control knobs for the respective frequency subbands and when changing from a standard stereophonic system to a simulated 4-channel system, the various knobs of the GEQ often correspond to different frequency subbands and this, of course, leads to difficulties of operation. By way of example, when the signals of a stereophonic program source having a left and right channels are divided into high frequency signals and low frequency signals for the respective channels to provide a simulated 4-channel system, each of the GEQs for the left and right channels must be divided according to the frequency of the two different speakers for that channel, while the GEQ for each channel operates normally in the stereophonic system. Therefore, the operator must determine which of the control knobs of the two GEQs are for each of the four speakers when listening to the sound program in a simulated 4-channel mode.
In order to let the operator recognize which knobs correspond to which uses more easily, the control panel of the car stereo often indicates the various uses for the control knobs with letters, symbols or the like. In general, however, the car stereo is installed in the dashboard or the like of the automobile, and thus the area of the control panel must be made as small as possible. Therefore, there is minimal space for the control panel of the GEQ and the various symbols used to identify the control knobs are often eliminated or, if present, are often not easily readable, and satisfactory operation is thus difficult to attain.